Synthesis and conjugation of Sr2MgSi2O7:Eu2+, Dy3+ water soluble afterglow nanoparticles for photodynamic activation

• Sr3MgSi2O8:Eu2+, Dy3+ water soluble nanoparticles are synthesized by Sol-Gel method following by coating with APTES.
• The surface coating with APTES and the conjugation with PpIX and folic acid improve their water solubility.
• The surface coating and the conjugation also enhance the PpIX luminescence 10 times and singlet oxygen production.
• The surface coating and conjugation largely increase the cell uptake and greatly reduce their dark cytotoxicity.
• Sr3MgSi2O8:Eu2+, Dy3+/PPIX/Folic acid nanoconjugates are promising for X-ray induced photodynamic therapy on cancer treatment.

The applications of afterglow particles for photodynamic activation and biological imaging have become a topical research area. For these applications, it is critical to have water soluble nanoparticles. However, the synthesis of water soluble afterglow nanoparticles like Sr2MgSi2O7:Eu2+, Dy3+ is a challenging issue because most afterglow materials are very complicated in composition that cannot be synthesized by simple chemical routes. Here, for the first time, Sr2MgSi2O7:Eu2+, Dy3+ water soluble and stable nanoparticles are synthesize using a modified Sol-Gel method followed by the grinding and coating with APTES. The surface coating of the afterglow with APTES and the conjugation with PpIX and folic acid not only improve their water solubility but also enhance the PpIX luminescence by 10 times. More importantly, these strategies make it possible to produce singlet oxygen under X-ray irradiation, which is a very important result for deep cancer treatment. In addition, the surface coating and conjugation largely increase the cell uptake and greatly reduce their dark cytotoxicity. All these results indicate the methods reported here for afterglow nanoparticle synthesis, coating and conjugation are successful, and consequently, the prepared Sr2MgSi2O7:Eu2+, Dy3+/PPIX/Folic acid nano-conjugates are promising for X-ray induced photodynamic therapy on cancer treatment.